CN109327246B

CN109327246B - Mobile communication system, radio station, core network and method thereof

Info

Publication number: CN109327246B
Application number: CN201811323668.4A
Authority: CN
Inventors: 二木尚; 网中洋明
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2012-12-28
Filing date: 2013-12-02
Publication date: 2022-02-08
Anticipated expiration: 2033-12-02
Also published as: EP2941049A4; KR20170085608A; JP2019097184A; JPWO2014103176A1; EP3487220A3; EP3627896A1; EP3487220A2; EP2941049A1; CN104885516A; CN109392052A; KR20180063902A; JP6750694B2; SG10201701222QA; SG11201505087SA; KR20190016140A; US20220330101A1; US10548051B2; KR102056114B1; KR101864189B1; KR101947542B1

Abstract

The invention relates to a mobile communication system, a radio station, a core network and a method thereof. The radio network (6) and the radio terminal (4) are configured to, when the radio terminal (4) uses a first cell (10) served by the first radio station (1) as a primary cell and a second cell (20) served by the second radio station (2) as a secondary cell, change the secondary cell from the second cell (20) to a third cell (30) while maintaining communication state information on the radio terminal (4) on the second cell (20). Thus, for example, it is possible to cause a communication service in a secondary cell to continue after a secondary cell change when a radio terminal simultaneously using a plurality of cells served by different radio stations changes the secondary cell from a cell of one radio station to a cell of another radio station.

Description

Mobile communication system, radio station, core network and method thereof

The present application is a divisional application of applications with PCT application numbers PCT/JP2013/007044, international application number 2013, 12/2/20153, chinese application number 201380068731.3, entitled "radio communication system, radio station, radio terminal, communication control method, and computer readable medium" that entered the chinese country phase at 29/6/2015.

Technical Field

The present invention relates to a radio communication system in which a radio station and a radio terminal communicate with each other using a plurality of cells.

Background

In recent years, in order to improve communication quality and speed to further cope with the rapid growth of mobile data traffic, standardization of a Carrier Aggregation (CA) function that allows a radio base station (enodeb (enb)) and a radio terminal (user equipment (UE)) to communicate with each other using a plurality of cells has been discussed in 3GPP LTE (long term evolution). The cells that a UE can use in CA are limited to the cells of one eNB (i.e., the cells served by one eNB).

Cells used by the UE are classified into a primary cell (PCell), which has been used as a serving cell at the beginning of CA, and a secondary cell (SCell), which is additionally or dependently used. Non-access stratum (NAS) mobility information, security information (security input), and the like are transmitted and received through the PCell during radio connection (re) establishment (RRC connection establishment/re-establishment) (see non-patent document 1). The DL carrier corresponding to the PCell is a DL primary component carrier (DL PCC) and its corresponding UL carrier is an UL PCC. Similarly, the DL carrier corresponding to the SCell is a DL secondary component carrier (DL SCC), and its corresponding UL carrier is a UL SCC.

To enable the UE to use the SCell in CA, the eNB notifies the UE of configuration information (SCell configuration) for a candidate cell of the SCell and activates a cell actually used by the UE. The procedures of addition, release, activation, and deactivation of scells will be described in connection with fig. 17.

In step S1, the UE establishes an RRC connection (RRC connection setup) in cell 1 of the NB. Cell 1 is the PCell. At step S2, the eNB transmits configuration information to the UE, including a list of cells to be added as scells (cell 2 and cell 3 in this example) (RRC connection reconfiguration including SCell addition list). In step S3, the UE adds cell 2 and cell 3 as scells (SCell —

cell

2, 3 addition). At this time, the UE cannot transmit or receive data in cell 2 and cell 3. At step S4, the eNB transmits an instruction to activate cell 2 as an SCell (SCell — cell 2 activation control). In step S5, the UE activates cell 2(SCell — cell 2 activation). In this way, the UE and the eNB transmit and receive data using cell 1 and cell 2 (carrier aggregation on cell 1 and cell 2) at step S6.

At a specific time point (step S7), the eNB determines to use cell 3 instead of cell 2 as an SCell, and transmits an instruction to deactivate cell 2 and an instruction to activate cell 3(SCell 2 deactivation control and SCell 3 activation control) to the UE. At steps S8 and S9, the UE deactivates cell 2(SCell ═ cell 2 deactivation) and activates cell 3(SCell ═ cell 3 activation). In this way, the UE and the eNB transmit and receive data using cell 1 and cell 3 (carrier aggregation on cell 1 and cell 3) at step S10.

At a specific time point (step S11), the eNB determines that carrier aggregation is unnecessary and transmits an instruction for releasing the SCell (RRC connection reconfiguration including an SCell release list) to the UE. In step S12, the UE releases cell 2 and cell 3 from the SCell (SCell —

cell

2, 3 release).

Also, a concept of inter-eNB CA aggregating a plurality of cells served by different enbs has been proposed (non-patent document 3). For example, inter-eNB CA may use macro cells served by macro base stations (macro enbs (menbs)) and pico cells served by pico base stations (pico enbs (penbs)).

Further, a method has been proposed in which signals for a control plane including mobility management of a UE are transmitted and received using a macro cell having a wide coverage, and data plane signals such as user data are transmitted and received using a pico cell providing relatively better communication quality (non-patent document 5). This method is also called C/U separation.

Reference list

Non-patent document

[ non-patent document 1]3GPP TS 36.300 V11.3.0, "Evolved Universal Radio Access (E-UTRA) and Evolved Universal Radio Access Network (E-UTRAN); (ii) an Overall description; stage 2, "section 7.5, month 9 2012

[ non-patent document 2]3GPP TS 36.331 V11.1.0, "Evolved Universal Radio Access (E-UTRA); radio Resource Control (RRC); protocol specification, "section 5.3.5.4, 9 months 2012

[ non-patent document 3]3GPP TS 36.423 V11.2.0, "Evolved Universal Radio Access Network (E-UTRAN); x2 application protocol (X2AP), "section 9.1.1, month 9 2012

[ non-patent document 4]3GPP RWS-120046, Samsung Electronics, "Technologies for Rel-12 and Onwards,"3GPP TSG RAN Workshop on Rel-12 and Onwards Ljubljana, Slovenia, 6.6.12.2012

Disclosure of Invention

Technical problem

In inter-eNB CA, for example, a cell of a macro base station (macro eNB (menb)) and a cell of a low power base station (low power node (LPN)) are simultaneously used as a PCell and an SCell, respectively. In this case, the bearer is separately configured in the PCell and the SCell. The UE communicates with the MeNB over a bearer in the PCell and communicates with the LPN over a bearer in the SCell.

The inventors of the present application have conducted various studies on continuity of a communication service when a radio terminal (UE) performing inter-eNB CA moves between cells, and have found several problems. For example, the following will be considered: a UE performing inter-eNB CA using a cell of the MeNB as a PCell and a cell of the first LPN as an SCell changes the SCell to a cell of another second LPN. When an SCell change procedure (fig. 17) in normal CA (i.e., intra-eNB CA) is applied to the change of the SCell, the UE must release all information on the cell of the first LPN and newly configure information on the cell of the second LPN. Therefore, the following problems arise: communication service in the cell of the first LPN cannot continue in the cell of the second LPN after the SCell is changed.

Therefore, an object of the present invention is to provide a radio communication system, a radio station, a radio terminal, a communication control method, and a program, which contribute to enabling a communication service in a secondary cell to continue after a secondary cell change when a radio terminal simultaneously using a plurality of cells served by different radio stations changes the secondary cell from a cell of one radio station to a cell of another radio station.

Solution to the problem

In a first aspect, a radio communication system includes a radio terminal and a radio network including first to third radio stations. The first to third radio stations serve the first to third cells, respectively. The radio terminal has the following capabilities: while using a cell of one radio station as a primary cell, a cell of another radio station is used as a secondary cell. Also, the radio network and the radio terminal are configured to, when the radio terminal uses the first cell as a primary cell and the second cell as a secondary cell, change the secondary cell from the second cell to the third cell while maintaining communication state information on the radio terminal on the second cell.

In a second aspect, a first radio station includes a radio communication unit serving a first cell and a communication control unit. The communication control unit is configured to, when the radio terminal changes the secondary cell to a third cell served by a third radio station while using the first cell as a primary cell and using a second cell served by the second radio station as a secondary cell, perform at least one of: (a) transmitting a request to suspend data communication with the radio terminal in the second cell; and (b) receiving or transmitting communication status information on the second cell regarding the radio terminal.

In a third aspect, a second radio station includes a radio communication unit serving a second cell and a communication control unit. The communication control unit is configured to, when the radio terminal changes the secondary cell to a third cell served by a third radio station while using the first cell served by the first radio station as a primary cell and the second cell as a secondary cell, receive at least one of: (a) a request to suspend data communication with the radio terminal in the second cell; and (b) a request to transmit communication status information on the radio terminal on the second cell and to perform at least one of suspending the data communication and transmitting the communication status information.

In a fourth aspect, a third radio station includes a radio communication unit serving a third cell and a communication control unit. The communication control unit is configured to receive communication state information on the radio terminal on the second cell from the first radio station or the second radio station when the radio terminal changes the secondary cell to the third cell while using the first cell served by the first radio station as the primary cell and using the second cell served by the second radio station as the secondary cell.

In a fifth aspect, a radio terminal comprises: a radio communication unit configured to communicate with the first to third wireless power stations, and a communication control unit. The communication control unit is configured to perform control of using a second cell served by the second radio station as a secondary cell while using a first cell by the first radio station as a primary cell. The communication control unit is further configured to, when the first cell serves as a primary cell and the second cell serves as a secondary cell, change the secondary cell from the second cell to a third cell served by the third radio station while maintaining the communication state information on the second cell.

In a sixth aspect, a communication control method in a first radio station serving a first cell includes: when the radio terminal changes the secondary cell to a third cell served by a third radio station while using the first cell as a primary cell and using a second cell served by the second radio station as a secondary cell, performing at least one of: (a) transmitting a request to suspend data communication with the radio terminal in the second cell; and (b) receiving or transmitting communication status information on the second cell regarding the radio terminal.

In a seventh aspect, a communication control method in a second radio station serving a second cell includes: when the radio terminal changes the secondary cell to a third cell served by a third radio station while using the first cell served by the first radio station as a primary cell and the second cell as a secondary cell, receiving at least one of: (a) a request to suspend data communication with the radio terminal in the second cell; and (b) a request to transmit communication status information on the radio terminal on the second cell and to perform at least one of suspending the data communication and transmitting the communication status information.

In an eighth aspect, a communication control method in a third radio station serving a third cell includes: when the secondary cell is changed to a third cell while the radio terminal uses a first cell served by the first radio station as a primary cell and uses a second cell served by the second radio station as a secondary cell, communication state information on the radio terminal on the second cell is received from the first radio station or the second radio station.

In a ninth aspect, a communication control method in a radio terminal includes: (a) using a second cell served by a second radio station as a secondary cell while using a first cell of the first radio station as a primary cell; and (b) when the first cell is used as a primary cell and the second cell is used as a secondary cell, changing the secondary cell from the second cell to a third cell served by the third radio station while maintaining the communication state information on the second cell.

In a tenth aspect, a program includes instructions for causing a computer to execute the communication control method according to the above-described sixth aspect.

In an eleventh aspect, a program includes instructions for causing a computer to execute the communication control method according to the seventh aspect described above.

In a twelfth aspect, a program includes instructions for causing a computer to execute the communication control method according to the above-described eighth aspect.

In a thirteenth aspect, a program includes instructions for causing a computer to execute the communication control method according to the above-described ninth aspect.

Advantageous effects of the invention

According to the aspects, it is possible to provide a radio communication system, a radio station, a radio terminal, a communication control method, and a program capable of enabling a communication service in a secondary cell to continue after a secondary cell change when a radio terminal simultaneously using a plurality of cells served by different radio stations changes the secondary cell from a cell of one radio station to a cell of another radio station.

Drawings

Fig. 1 is a diagram illustrating a configuration example of a radio communication system according to a first embodiment.

Fig. 2 is a diagram illustrating a configuration example of a first radio station according to the first embodiment.

Fig. 3 is a diagram illustrating a configuration example of a second radio station according to the first embodiment.

Fig. 4 is a diagram illustrating a configuration example of a third radio station according to the first embodiment.

Fig. 5 is a diagram illustrating a configuration example of a radio terminal according to the first embodiment.

Fig. 6 is a flowchart illustrating an operation example of a radio terminal according to the first embodiment (procedure example 1).

Fig. 7 is a flowchart illustrating an operation example of a radio network according to the first embodiment (procedure example 1).

Fig. 8 is a sequence diagram illustrating an example of a communication control method in a radio communication system according to the first embodiment (procedure example 1).

Fig. 9 is a sequence diagram illustrating another example of a communication control method in a radio communication system according to the first embodiment (modification of the process example 1).

Fig. 10 is a flowchart illustrating an operation example of a radio terminal according to the first embodiment (procedure example 2).

Fig. 11 is a flowchart illustrating an operation example of the first radio station according to the first embodiment (process example 2).

Fig. 12 is a flowchart illustrating an operation example of the second radio station according to the first embodiment (process example 2).

Fig. 13 is a sequence diagram illustrating an example of a communication control method in a radio communication system according to the first embodiment (procedure example 2).

Fig. 14 is a sequence diagram illustrating an example of a communication control method in a radio communication system according to the second embodiment (procedure example 3).

Fig. 15 is a sequence diagram illustrating an example of a communication control method in a radio communication system according to the second embodiment (procedure example 4).

Fig. 16 is a sequence diagram illustrating an example of a communication control method in a radio communication system according to the second embodiment (procedure example 5).

Fig. 17 is a sequence diagram illustrating a handover procedure in carrier aggregation of LTE (background art).

Detailed Description

Hereinafter, specific embodiments will be described in detail with reference to the accompanying drawings. In the respective drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant description thereof will not necessarily be provided for clarification of the description.

First embodiment

Fig. 1 illustrates a configuration example of a radio communication system according to the embodiment. The radio communication system according to the embodiment includes a radio network 6 and a radio terminal 4. The radio network 6 comprises a first radio station 1, a second radio station 2, a third radio station 3, and a core network 5 connected to the radio stations 1 to 3. The

radio stations

1, 2 and 3 serve a first cell 10, a second cell 20 and a third cell 30, respectively. The radio stations 1 to 3 are for example radio base stations or base station controllers. The radio terminal 4 has the capability of using a cell of one radio station as a primary cell (PCell) while using a cell of another radio station as a secondary cell (SCell). In other words, the radio terminal 4 supports carrier aggregation over multiple cells served by different radio stations. A primary cell (PCell) is a cell that has been used as a serving cell for a radio terminal 4 at the beginning of carrier aggregation. A secondary cell (SCell) is a cell that is additionally or dependently used for carrier aggregation in the radio terminal 4.

For example, the radio terminal 4 may establish a second radio connection in the second cell 20 while maintaining the first radio connection in the first cell 10, and may use the first cell 10 as a primary cell (PCell) and the second cell 20 as a secondary cell (SCell). In this manner, radio terminal 4 may use multiple cells (e.g., cells 10 and 20) simultaneously in order to transmit or receive signals (e.g., user data or control information). The expression "simultaneously using a plurality of cells" is not limited to the case where signals are actually received or transmitted simultaneously in a plurality of cells. The expression may refer to a case where a signal is actually received or transmitted only in one or a few cells but a state in which a signal can be received or transmitted in all of a plurality of cells is generated. The expression may also refer to the case where different kinds of signals are received or transmitted in the respective cells. Alternatively, the expression may refer to a case where each of a plurality of cells is used to receive or transmit a signal. From the perspective of carrier aggregation over multiple cells served by different radio stations, the ability to use multiple cells served by different radio stations may be referred to as inter-radio station carrier aggregation. Further, from the perspective of simultaneous use of multiple cells, the ability to use multiple cells served by different radio stations may be referred to as Dual Connectivity (Dual Connection), Multi-Connectivity (Multi-Connection), or the like.

The radio terminal 4 may transmit a terminal capability report to the radio station indicating that inter-radio station carrier aggregation is supported, or may implicitly indicate that inter-radio station carrier aggregation is supported by the class, device release number, etc. of the radio terminal 4. Also, as described above, the capability of inter-radio station carrier aggregation may be referred to as dual connection capability or multi-connection capability.

Fig. 1 illustrates a heterogeneous network (HetNet) environment. Specifically, the first cell 10 illustrated in fig. 1 has a wider coverage than the second cell 20 and the third cell 30. Specifically, the first cell 10 illustrated in fig. 1 has a wider coverage than the second cell 20 and the third cell 30. Also, fig. 1 illustrates a hierarchical cell structure in which a second cell 20 is disposed near a boundary between a first cell 10 and a third cell. However, the cell structure illustrated in fig. 1 is only an example. In some implementations,

cells

10, 20, and 30 may have the same degree of coverage. In other words, the radio communication system according to the embodiment can be applied to a homogeneous network environment.

The radio communication system according to this embodiment operates in such a manner that, when the radio terminal 4 performs inter-radio-station carrier aggregation on the cells 10 and 20, data communication (also referred to as a data communication service, a communication service, or simply a service) that has been provided in the SCell (i.e., the cell 20) continues even after the SCell is changed from the cell 20 to the cell 30. That is, when the radio terminal 4 uses the first cell 10 as a PCell and the second cell 20 as an SCell, the radio terminal 4 and the radio network 6 perform the following procedure: the SCell is changed from the second cell 20 to the third cell 30 while maintaining (storing) communication state information on the second cell 20 regarding the radio terminal 4. The radio terminal 4 and the radio network 6 may maintain the communication state information on the cell 20 without the communication state information during the execution of the SCell change procedure. Here, the continuity of data communication may refer to continuity in a strict sense, or may refer to continuity of a service performed by data communication. Also, if transmission of a specific packet through the cell 20 fails, the continuity of data communication may refer to retransmission of the packet through the cell 20 or 30.

More specifically, when performing inter-radio station carrier aggregation using the cell 10 as the PCell and the cell 20 as the SCell, the radio terminal 4 changes the SCell from the second cell 20 to the third cell 30 while maintaining communication state information on the second cell 20 (i.e., the SCell). Also, after changing the SCell to the third cell 30, the radio terminal 4 resumes communication based on the communication state information held therein. That is, the radio terminal 4 recovers continuity of data communication (also referred to as a data communication service, a communication service, or simply a service) that has been provided in the second cell 20 as the SCell in the third cell 30.

When inter-radio-station carrier aggregation is performed by the radio terminal 4 using the cell 10 as a PCell and the cell 20 as an SCell, the radio network 6 changes the SCell of the radio terminal 4 from the second cell 20 to a third cell while maintaining communication state information on the radio terminal 4 on the second cell 20. Also, after changing the SCell of the radio terminal 4 to the third cell 30, the radio network 6 resumes communication based on the communication state information held therein. That is, the radio network 6 restores, in the third cell 30, the continuity of data communication (also referred to as a data communication service, a communication service, or simply a service) that has been provided in the second cell 20 as the SCell.

Accordingly, the radio communication system can allow continuity of data communication performed in the cells 10 and 20 even after the SCell is changed to the cell 30 of the radio station 3 when the radio terminal 4 performs data communication (also referred to as a data communication service, a communication service, or simply referred to as a service) using the cell 10 and the cell 20 of the

radio stations

1 and 2 as the SCell and the SCell, respectively.

In the above description, during execution of the procedure for changing the SCell of radio terminal 4, radio terminal 4 and radio network 6 may continue or suspend data communication (referred to as a data communication service, a communication service, or simply a service) in the PCell.

In the above description, the third radio station 3 may be the same as the first radio station 1. In other words, the first cell 10 and the third cell 30 may be different cells or sectors provided by one radio station 1.

The communication state information held in the radio terminal 4 and the SCell (cell 20) in the radio network 6 may be information required for data communication (referred to as a data communication service, a communication service, or simply a service) performed in the SCell (cell 20) before the change is resumed in the SCell after the change. Thus, the communication state information on the SCell may contain, for example, content similar to the communication state information on the source cell, which is transmitted from the source cell radio station to the target cell radio station during normal handover. The communication state information on the SCell may be referred to as information indicating a communication state or service state of the radio terminal 4 on the SCell. The communication state information on the SCell may be a communication state of each service, or may be a communication state of a plurality of services. The communication status information may comprise, for example, at least one of the following information elements:

-a transmission or reception state of user data (user plane (U-plane));

-service information;

-carrying information; and

-radio resource configuration information.

Here, the bearer is, for example, a Signaling Radio Bearer (SRB), a Data Radio Bearer (DRB), or a network bearer (S1 bearer, E-RAB, or EPS bearer).

The radio terminal 4 may maintain communication state information on the SCell while changing the SCell as follows. Radio terminal 4 may release the bearer in second cell 20 configured for radio terminal 4 (SCell bearer) and maintain the communication state information. Alternatively, the radio terminal 4 may release the bearer in the second cell 20(SCell bearer), but may retain the configuration information and communication state information of the bearer in the second cell. When releasing the SCell bearer, radio terminal 4 may consider and process information about the SCell bearer as if it were information about a bearer in the first cell 10 configured for radio terminal 4 (PCell bearer). For example, radio terminal 4 may process bearer configuration information excluding radio bearer configuration, similar to PCell bearers. In other words, processes such as maintenance, update, reset, or reconfiguration of SCell bearer configuration information may be performed similarly to PCell bearer configuration information. The PCell bearer (or SCell bearer) may be, but is not limited to, a radio bearer or a network bearer configured in the PCell (or SCell).

The radio network 6 may maintain communication state information on the SCell by the same method as the radio terminal 4. That is, the radio network 6 may release the bearer (SCell bearer) in the second cell 20 configured for the radio terminal 4 and may maintain the communication state information. Alternatively, the radio network 6 may release the bearer in the second cell 20(SCell bearer), but may maintain the configuration information and communication state information about the bearer in the second cell. When releasing the SCell bearer, the radio network 6 may reconfigure the released SCell bearer as a bearer in the first cell 10(PCell bearer) to thereby treat the released SCell bearer as a PCell bearer. For example, the radio network 6 may change the SCell bearer to the PCell bearer by switching the path (route) of the SCell bearer to the PCell, and may inherit configuration information about the SCell bearer to the PCell bearer. That is, bearer configuration information on the SCell bearer is inherited to the PCell bearer. In this case, the radio bearer configuration may be excluded from the inherited information.

Hereinafter, data communication will be described as a broad meaning service. From the perspective of the radio network, services referred to herein include, but are not limited to, transmission of downlink data and control plane signaling, reception of uplink data and control plane signaling, and transmission and reception of downlink and uplink voice calls. Similarly, from the perspective of a radio terminal, services include, but are not limited to, the reception of downlink data and control signals, the transmission of uplink data and control signals, and the reception and transmission of downlink and uplink voice calls. Hereinafter, embodiments of the present invention are basically described by way of examples of downlink services. However, the present invention can naturally be applied to an uplink service.

Next, a configuration example of the radio stations 1 to 3 and the radio terminal 4 according to this embodiment will be described. Fig. 2 is a block diagram illustrating a configuration example of the first radio station 1. The radio communication unit 11 receives an uplink signal transmitted from the radio terminal 4 via an antenna. The received data processing unit 13 recovers the received uplink signal. The obtained received data is transmitted via the communication unit 14 to another network node (e.g. a data transmission means or a mobility management means in the core network 5) or to another radio station. For example, uplink user data received from the radio terminal 4 is transferred to a data transfer device in the core network 5. Also, non-access stratum (NAS) control data among the control data received from the radio terminal 4 is transmitted to the mobility management means in the core network 5. Further, the received data processing unit 13 receives control data to be transmitted to the

radio station

2 or 3 from the communication control unit 15, and transmits the control data to the

radio station

2 or 3 via the communication unit 14.

The transmission data processing unit 12 acquires user data destined for the radio terminal 4 from the communication unit 14, and performs processing such as error correction coding, rate matching, and interleaving to generate a transmission channel. Further, the transmission data processing unit 12 then generates a transmission symbol sequence by adding control information to the data sequence of the transmission channel. The radio communication unit 11 generates a downlink signal by performing processing such as carrier modulation, frequency conversion, and signal amplification based on the transmission symbol sequence, and transmits the generated downlink signal to the radio terminal 4. Also, the transmission data processing unit 12 receives control data to be transmitted to the radio terminal 4 from the communication control unit 15, and transmits the control data to the radio terminal 4 via the radio communication unit 11.

The communication control unit 15 controls inter-radio station carrier aggregation, which uses the first cell 10 as a PCell and the second cell 20 as an SCell. Further, the communication control unit 15 performs the following process: this procedure is used to change the SCell of the radio terminal 4 from the second cell 20 to the third cell 30 while maintaining communication state information on the radio terminal 4 on the SCell (second cell 20) in the radio network 6 and the radio terminal 4. The communication control unit 15 performs an SCell change procedure in cooperation with the radio station 2, the radio station 3, and the radio terminal 4.

In an example, the communication control unit 15 may receive communication status information on the radio terminal 4 on the SCell (second cell 20) from the second radio station 2, and then transmit the communication status information to the third radio station 3. Also, the communication control unit 15 may request the core network 5 or the second radio station 2 to switch the bearer in the cell 20(SCell bearer) to the bearer in the cell 10(PCell bearer). Details of the control and signaling performed by the communication control unit 15 will be described later.

Fig. 3 is a block diagram illustrating a configuration example of the second radio station 2. The functions and operations of the radio communication unit 21, the transmission data processing unit 22, the reception data processing unit 23, and the communication unit 24 illustrated in fig. 3 are similar to those of the respective elements (i.e., the radio communication unit 11, the transmission data processing unit 12, the reception data processing unit 13, and the communication unit 14) of the radio station 1 illustrated in fig. 2.

The communication control unit 25 of the radio station 2 controls inter-radio station carrier aggregation, which uses the first cell 10 as a PCell and the second cell 20 as an SCell. Further, the communication control unit 25 performs the following processes: this procedure is used to change the SCell of the radio terminal 4 from the second cell 20 to the third cell 30 while maintaining communication state information on the radio terminal 4 on the SCell (second cell 20) in the radio network 6 and the radio terminal 4. The communication control unit 25 performs an SCell change procedure in cooperation with the radio station 1, the radio station 3, and the radio terminal 4.

In an example, the communication control unit 25 may be operable to transmit communication status information on the SCell (second cell 20) regarding the radio terminal 4 to the first radio station 1, the third radio station 3, or the core network 5. The communication control unit 25 may suspend the provision of the service to the radio terminal 3 in the Scell (second cell 20), maintain the communication state information on the second cell 20 with respect to the radio terminal 3 without releasing (deleting) the communication state information even after the suspension of the service, and transmit the communication state information to the first radio station 1, the third radio station 3, or the core network 5 after the Scell is changed to the third cell 30. Further, the communication control unit 25 may request the core network 5 or the first radio station 1 to switch the bearer in the cell 20 (referred to as SCell bearer or secondary bearer) to the bearer in the cell 10 (referred to as PCell bearer or primary bearer). Details of the control and signaling performed by the communication control unit 25 will be described later.

Fig. 4 is a block diagram illustrating a configuration example of the third radio station 3. The functions and operations of the radio communication unit 31, the transmission data processing unit 32, the reception data processing unit 33, and the communication unit 34 illustrated in fig. 4 are similar to those of the respective elements (i.e., the radio communication unit 11, the transmission data processing unit 12, the reception data processing unit 13, and the communication unit 14) of the radio station 1 illustrated in fig. 2.

The communication control unit 35 of the radio station 3 performs the following processes: this procedure is used to change the SCell of the radio terminal 4 from the second cell 20 to the third cell 30 while maintaining communication state information on the radio terminal 4 on the SCell (second cell 20) in the radio network 6 and the radio terminal 4. The communication control unit 35 performs an SCell change procedure in cooperation with the radio station 1, the radio station 2, and the radio terminal 4.

In an example, the communication control unit 35 may receive communication state information on the radio terminal 4 on the SCell (second cell 20) from the first radio station 1, the second radio station, or the core network 5. The communication control unit 35 may perform control to allow the service already provided in the SCell (i.e., the second cell 20) before the change to be provided in the SCell (i.e., the third cell 30) after the change based on the communication state information on the SCell. Details of the control and signaling performed by the communication control unit 35 will be described later.

Fig. 5 is a block diagram illustrating a configuration example of the radio terminal 4. The radio communication unit 41 supports carrier aggregation over a plurality of cells served by different radio stations, and can transmit or receive user data using a plurality of cells (e.g., cells 10 and 20) at the same time. Specifically, the radio communication unit 41 receives a downlink signal from the radio station 1, the radio station 2, or the radio station 3 via an antenna. The received data processing unit 42 recovers the received data from the received downlink signal and transmits the received data to the data control unit 43. The data control unit 43 uses the received data according to its purpose. The transmission data processing unit 44 and the radio communication unit 41 generate an uplink signal using the transmission data supplied from the data control unit 43 and transmit the uplink signal to the radio station 1, the radio station 2, or the radio station 3.

The communication control unit 45 controls inter-radio station carrier aggregation using the first cell 10 as a PCell and using the second cell 20 as an SCell. Further, the communication control unit 45 performs the following process: this procedure is used to change the SCell of the radio terminal 4 from the second cell 20 to the third cell 30 while maintaining communication state information on the radio terminal 4 on the SCell (second cell 20) in the radio network 6 and the radio terminal 4. The communication control unit 45 executes the SCell change procedure in cooperation with the radio station 1, the radio station 2, and the radio station 3.

In an example, the communication control unit 45 may change the SCell from the first cell 10 to the third cell 30 while maintaining communication state information about the radio terminal 4 on the SCell (second cell 20). Specifically, the communication control unit 45 may maintain the communication state information on the radio terminal 4 on the SCell (second cell 20) without releasing the communication state information during the execution of the SCell change procedure (e.g., handover procedure). The communication control unit 45 may recover, in the SCell after the change (i.e., the third cell 30), the service provided in the SCell before the change (i.e., the second cell 20). Details of the control and signaling performed by the communication control unit 45 will be described later.

Hereinafter, process examples 1 and 2 of the communication control method in the radio communication system according to the present embodiment will be described.

(Process example 1)

In process example 1, the radio terminal 4 and the radio network 6 maintain the communication state information on the radio terminal 4 on the SCell before the change (i.e., the second cell 20) while changing the SCell of the radio terminal 4 from the second cell 20 to the third cell 30, and then resume the communication (service) that has been provided in the SCell before the change (i.e., the second cell 20) in the SCell after the change (i.e., the third cell 30).

Fig. 6 is a flowchart illustrating an example of the operation of radio terminal 4 according to process example 1. In step S101, the radio terminal 4 (communication control unit 45) receives an instruction to change the Scell to the third cell 30 from the radio network 6. In step S102, the radio terminal 4 (communication control unit 45) initiates a procedure for changing the SCell to the cell 30 while maintaining the communication state information on the cell 10. When the change of the SCell is completed (yes in step S103), the radio terminal 4 (communication control unit 45) resumes the communication of the SCell in the cell 30 based on the communication state information on the cell 20 that is maintained. The resumed communication includes communication that has been performed in the SCell (cell 20) before the change.

Fig. 7 is a flowchart illustrating an example of the operation of the radio network 6 according to process example 1. At step S201, the radio network 6 (e.g., the communication control unit 15 of the radio station 1) transmits an instruction to change the SCell to the third cell 30 to the radio terminal 4. In step S202, while maintaining the communication state information on the radio terminal 4 on the cell 20, the radio network 6 (e.g., the communication control unit 15 of the radio station 1, the communication control unit 25 of the radio station 2, and the communication control unit 35 of the radio station 3) initiates a procedure for changing the SCell of the radio terminal 4 to the cell 30. When the change of the SCell is completed (yes in step S203), the radio network 6 (communication control unit 35) resumes the communication of the radio terminal 4 in the SCell after the change (i.e., cell 30) based on the communication state information about the radio terminal 4 held on the cell 20. The resumed communication includes communication that has been performed in the SCell (cell 20) before the change.

Fig. 8 is an example of a sequence diagram illustrating the overall processing of procedure example 1. In steps S301 and S302, the radio network 6 and the radio terminal 4 perform communication (inter-radio station carrier aggregation) using the first cell 10 as a PCell and using the second cell 20 as an SCell. At step S303, the radio network 6 transmits an instruction to the radio terminal 4 to change the SCell from the cell 10 to the cell 30. At step S304, the radio terminal 4 initiates a change of SCell to cell 30 while maintaining communication state information on cell 20. The radio network 6 also maintains communication state information on the radio terminal 4 on the cell 20 during the change of the SCell of the radio terminal 4 (step S305). At step S306, the radio network 6 and the radio terminal 4 complete the SCell change of the radio terminal 4 from the cell 20 to the cell 30. In step S307, the radio network 6 and the radio terminal 4 resume communication of the radio terminal 4 in the cell 30 based on the communication state information on the radio terminal 4 held on the cell 20. The resumed communication includes communication that has been performed in the SCell (cell 20) before the change.

In the above-described process example 1, the first radio station 1 (communication control unit 15) can explicitly notify the radio terminal 4 of the communication state information held on the second cell 20 (or perform SCell change while holding the communication state information). The notification may be transmitted together with an instruction message for changing the PCell from the second cell 10 to the third cell 30, or may be transmitted using a message different from the PCell change instruction. Also, the first radio station 1 (communication control unit 15) may notify the radio terminal 4 to release a bearer (SCell bearer) in the cell 20, or to hold the bearer configuration information but release the SCell bearer.

(Process example 2)

Process example 2 corresponds to a more specific example of process example 1 described above. Fig. 9 is a flowchart of an example of the operation of radio terminal 4 according to process example 2. In step S401, the radio terminal 4 (communication control unit 45) receives an instruction for changing the SCell to the third cell 30 from the first radio station 1 on the first cell 10. In step S402, the radio terminal 4 (communication control unit 45) holds communication state information of data communication (service B) that has been provided in the SCell (second cell 10). At step S403, the radio terminal 4 (communication control unit 45) initiates a change of the SCell from the second cell 20 to the third cell 30. When the change of the SCell is completed (yes in step S404), the radio terminal 4 (communication control unit 45) continues data communication that has been performed in the SCell before the change in the cell 30 (service B) based on the communication state information on the cell 20 that is maintained. That is, the radio terminal 4 (communication control unit 45) resumes the service B.

Fig. 10 is a flowchart illustrating an example of the operation of the first radio station 1 according to process example 2. In step S501, the radio station 1 (communication control unit 15) transmits to the radio station 2 an instruction for suspending the service B to the radio terminal 4 and an instruction for reporting communication state information on the radio terminal 4. Here, the service suspend instruction and the communication state information report instruction may be transmitted using the same message, or may be transmitted using separate messages. In step S502, the radio station 1 (communication control unit 15) receives a report on the communication state information of the radio terminal 4 on the second cell 20 from the radio station 2. In step S503, the radio station 1 (communication control unit 15) transmits an instruction to change the SCell to the third cell 30 to the radio terminal 4. In step S504, the radio station 1 (communication control unit 15) determines whether the change of the SCell and the preparation for using the third cell have been completed. When the change of the SCell and the preparation for using the third cell have been completed (yes in step S504), the radio station 1 (communication control unit 15) transmits communication state information on the second cell 20 regarding the radio terminal 4 to the third radio station 3 (step S505).

In step S501 of fig. 10, the instruction for causing the second radio station to suspend service B may be transmitted using the same or a different message as the instruction for reporting communication status information on the second cell.

At step S503 of fig. 10, the instruction for the radio terminal 4 to change the SCell to the third radio station 3 may include configuration information (e.g., radio resource configuration information) of the third cell 30. The configuration information of the third cell 30 may have the same contents as the configuration information of the second cell that is the SCell. The first radio station 1 can acquire configuration information of the third cell 30 from the third radio station 3 in advance.

At step S504 of fig. 10, the first radio station 1 may determine completion of the SCell change based on receiving an affirmative response (ACK) to the SCell change instruction from the radio terminal 4. Alternatively, the first radio station 1 may determine the completion of the SCell change based on receiving a message from the radio terminal 4 indicating the completion of the SCell change.

The transmission of the communication state information of the second cell 20 to the third radio station 3 at step S505 of fig. 10 may be performed before completion of the SCell change (i.e., before step S504 of fig. 10).

The transmission of the communication state information of the second cell 20 to the third radio station 3 (step S505) may be used as an instruction (or request) for using the third cell 30 as an SCell for the radio terminal 4. However, alternatively, the instruction to use the third cell 30 as an SCell for the radio terminal 4 may be transmitted in a separate message.

Fig. 11 is a flow chart illustrating an example of the operation of the second radio station 2 according to process example 2. In step S601, the radio station 2 (communication control unit 25) receives, from the radio station 1, an instruction for suspending a service for the subject radio terminal (i.e., radio terminal 4) and an instruction for reporting communication state information about the radio terminal 4. In step S602, the radio station 2 (communication control unit 25) suspends the provision of the service to the radio terminal 4 in the second cell 20. In step S603, the radio station 2 (communication control unit 25) transmits communication state information on the radio terminal 4 on the second cell 20 to the radio station 1.

Fig. 12 is a flow chart illustrating an example of the operation of the third radio station 3 according to process example 2. In step S701, the radio station 3 (communication control unit 35) completes preparation for allowing the subject radio terminal (i.e., the radio terminal 4) to use the third cell 30 as the SCell in cooperation with the first radio station 1. In step S702, the radio station 3 (communication control unit 35) receives communication state information on the radio terminal 4 on the cell 20 from the radio station 1. In step S703, the radio station 3 (communication control unit 35) recovers, in the third cell 30, the service B that has been performed on the radio terminal 4 in the SCell before the change (i.e., cell 20), based on the communication state information on the radio terminal 4 on the cell 20.

Fig. 13 is an example of a sequence diagram illustrating the overall processing of procedure example 2. In step S801, the radio station 1 and the radio terminal 4 perform communication using the first cell 10 as a PCell (service a). In step S802, the radio station 2 and the radio terminal 4 perform communication using the second cell 20 as an SCell (service B). In step S803, the radio station 1 transmits an instruction to suspend the service B and an instruction to report the communication status information to the radio station 2. In step S804, in response to the service suspension instruction, the radio station 2 suspends the service B for the radio terminal 4 in the SCell (second cell 20). In step S805, in response to the instruction for reporting communication status information, the radio station 2 reports communication status information on the second cell 20 about the radio terminal 4 to the radio station 1.

In step S806, the radio station 1 transmits an SCell change instruction to the radio terminal 4. In step S807, the radio terminal 4 suspends service B in the second cell 20, retains communication state information on the second cell 20, and initiates a procedure for changing the SCell to the third cell 30. In step S808, the radio station 1 and the radio station 3 complete preparation for using the third cell 30. In step S809, the radio station 1 and the radio terminal 4 complete the SCell change from the second cell 20 to the third cell 30. In step S810, the radio station 1 transmits communication status information on the second cell 20 about the radio terminal 4 to the radio station 3. In step S811, the radio station 3 and the radio terminal 4 perform communication (service B) in the cell 30 that has been performed in the SCell (i.e., cell 20) before the change.

(modification of Process example 2)

In the above-described process example 2, an example has been illustrated in which the communication state information on the second cell 20 about the wireless terminal 4 is transmitted from the second radio station 2 to the third radio station 3 via the first radio station 1. Alternatively, however, the second radio station 2 may transmit the communication status information directly to the third radio station 3 without via the first radio station 1. In an example, the first radio station 1 may request the second radio station 2 to send communication status information on the second cell 20 about the radio terminal 4 to the third radio station 3. In this case, the second radio station 2 can transmit the communication state information to the third radio station 3 in response to a request from the first radio station 1. In another example, the third radio station 3 may request the second radio station 2 to transmit communication status information on the second cell 20 about the radio terminal 4. In this case, the second radio station 2 can transmit the communication state information to the third radio station 3 in response to a request from the third radio station 3.

The communication (service) performed by the wireless terminal 4 in the above-described procedure examples 1 and 2 may be data communication (user plane (U-plane)) or may be control plane signaling (control plane (C-plane)).

In the above process examples 1 and 2, the exchange of messages and information between radio stations may be performed by the core network 5.

In the above-described process examples 1 and 2, during the execution of the SCell change procedure, the radio terminal 4 and the radio network 6 may continue or suspend communication in the PCell (service a).

In the above-described process examples 1 and 2, the instruction to change the SCell to the third cell may be an instruction to change the SCell from the second cell 20 to the third cell 30, or alternatively, may be an instruction to delete (release) the second cell 20 and add (or configure) the third cell 30.

In the above-described procedure example 2, the service a and the service B may be the same service.

In the above procedure example 2, the radio terminal 4 may perform a plurality of services in the PCell (cell 10). Similarly, the radio terminal 4 may perform a plurality of services in the SCell (i.e., cell 20) before the change. For example, the radio terminal 4 may perform services B and C in the SCell (i.e., cell 20) before the change. The radio terminal 4 can perform all services (e.g., both services B and C) that have been performed in the SCell before the change (i.e., cell 20) in the SCell after the change (i.e., cell 30). Alternatively, the radio terminal 4 may perform only a part of the services (e.g., only service B) that have been performed in the SCell before the change (i.e., cell 20) in the SCell after the change (i.e., cell 30).

The above-described process examples 1 to 2 can be applied to, but are not limited to, the case where the first radio station 1 is a radio station serving (managing) a cell having a relatively large coverage, and the second radio station 2 and the third radio station 3 are low-power radio stations (low-power nodes (LPNs)) serving (managing) a cell having a small coverage. Examples of the LPN include a radio station having the same function as the radio station 1 and a new network node (new node) having less functions than the radio station 1. Also, the second cell 20 and the third cell 30 may be a new type cell (new cell type) different from the existing cell and using a new type carrier (new carrier type) different from the existing carrier.

Second embodiment

In this embodiment, the first embodiment described above is applied to an example of a 3GPP LTE system. A configuration example of the radio communication system according to the present embodiment may be similar to that illustrated in fig. 1. However, the radio stations 1 to 3 correspond to enbs, the radio terminal 4 corresponds to a UE, and the core network 5 corresponds to an evolved packet core (RAN). Further, eNB1 to eNB3 correspond to a Radio Access Network (RAN). The transmission and reception of information between radio stations (i.e., between enbs) may use an X2 interface, which is a direct interface, may use an S1 interface through a core network, or may use a newly defined interface (e.g., an X3 interface). The radio terminals (UE)4 support carrier aggregation (inter-eNB CA) over multiple cells served by different radio stations (enbs). The expression "inter-eNB CA" is not limited to the case where signals are actually received or transmitted simultaneously in the cells of different enbs. The expression may refer to the following cases: although a state is generated in which signals (e.g., user data or control information) can be received or transmitted in all cells of different enbs, signals are actually received or transmitted in cells of several enbs. The expression may also refer to the case where different kinds of signals are received or transmitted in respective cells of different enbs. Alternatively, the expression may refer to a case where each of the cells of different enbs is used to receive or transmit a signal. In the following description, the radio stations 1 to 3 are referred to as eNB1 to eNB3, the radio terminal 4 is referred to as UE 4, and the core network 5 will be referred to as EPC 5.

As described in the first embodiment, the communication state information may include, for example, at least one of the following information elements:

-a transmission or reception state of user data (user plane (U-plane));

-service information;

-carrying information; and

-radio resource configuration information.

The transmission or reception status of user data may be, for example, the content of a SN status transfer message that transfers information indicating the status of a Packet Data Convergence Protocol (PDCP) Sequence Number (SN) and a Hyper Frame Number (HFN). The SN status transfer message includes an E-RAB ID, a reception status of UL PDCP SDU, a UL count value (PDCP SN + HFN), a DL count value (PDCP SN + HFN), and the like. Also, the transmission or reception state of the user data may be an RLC state (e.g., RLC status PDU).

The service information may include QoS information or a QoS Class Indicator (QCI) value.

The bearer information is information on a Signaling Radio Bearer (SRB), a Data Radio Bearer (DRB), or a network bearer (S1 bearer, E-RAB, or EPS bearer). The bearer information may include, for example, a bearer ID (e.g., drb-identity, eps-bearer identity, E-RAB ID), terminal identification information (e.g., eNB UE S1AP ID, MME UE S1AP ID, or TMSI), or network identification information (e.g., GUMMEI, UL GTP tunnel endpoint, or DL GTP tunnel endpoint).

The radio resource configuration information may include, for example, common radio resource configuration information (radio resource configuration common) or dedicated radio resource configuration information (radio resource configuration dedicated).

Next, process examples 3 to 5 of the communication control method in the radio communication system according to the present embodiment will be described.

(procedure example 3)

Process example 3 corresponds to process example 2 described in the first embodiment. That is, during a period in which the UE 4 experiences service a in the cell 10(PCell) of the eNB1 and service B in the cell 20(SCell) of the eNB2, when the SCell is changed to the cell 30 of the eNB3, the UE 4 and the radio network 6 (i.e., RAN and EPC) perform an SCell change while maintaining communication state information of the UE 4 on the cell 20. Also, the UE 4 and the radio network 6 perform service B in the SCell (i.e., cell 30) after the change. That is, the UE 4 and the radio network 6 resume service B.

Fig. 14 is an example of a sequence diagram illustrating the overall processing of procedure example 3. In fig. 14, the first cell 10 is denoted as cell 1, the second cell is denoted as cell 2, and the third cell 30 is denoted as cell 3. In step S901, the eNB1 and the UE 4 perform communication using the first cell 10 as a PCell (service a). At step S902, the eNB2 and the UE 4 perform communication using the second cell 20 as an SCell (serving B). At step S903, the eNB1 determines to change the SCell of the radio terminal 4 to the third cell 30, and transmits an instruction to abort the service B in the second cell 20 and instructions to report communication state information (an abort request for service and a communication state request) to the eNB 2. At step S904, the eNB2 suspends the service B in the cell 20 and transmits communication status information of the UE 4 on the cell 20 to the eNB 1. At step S905, the eNB1 transmits an SCell change instruction (RRC connection reconfiguration to. SCell change instruction (RRC connection reconfiguration) to the UE 4 including, for example, release (deconfiguration) of the cell 20 and configuration of the cell 30.

In steps S905 to S908, while maintaining the communication state information on the cell 20, the UE 4 releases the bearer in the cell 20 (releases the bearer in the cell 2) and reconfigures the bearer in the cell 30 (reestablishes the bearer in the cell 3). At step S909, eNB1 transmits an SCell preparation request to eNB 3. At step S910, the eNB3 prepares the cell 30 to provide the SCell to the radio terminal 4, and transmits a response to the SCell preparation request (SCell preparation request ACK) to the eNB 1. In step S911, the eNB1 transmits communication status information of the UE 4 on the cell 20 to the eNB 3.

In step S912, eNB1 and UE 4 complete the SCell change (RRC connection reconfiguration complete). At step S913, the eNB1 instructs the UE 4 to activate the third cell 30 as an SCell (cell 3 activation). At step S914, the eNB3 and the UE 4 resume service B in the SCell (i.e., cell 30) after the change.

In step S905 of fig. 14, transmission of the SCell change instruction from the eNB1 to the UE 4 is performed by transmitting an instruction to deconfigure the cell 20 and to configure the cell 30 using the RRC connection reconfiguration message. However, alternatively, the transmission of the SCell change instruction to the UE 4 may be performed by another method. For example, eNB1 may transmit instructions to UE 4 to delete cell 20 and add cell 30.

At step S905 of fig. 14, the eNB1 may explicitly inform the UE 4 to maintain the communication state information of the cell 20 (or perform SCell change while maintaining the communication state information) together with the RRC connection reconfiguration message or using a different message. Also in this case, eNB1 may inform UE 4 to release the bearer in cell 30.

The release of the SCell bearer by the UE 4 in step S907 of fig. 14 may be performed, for example, by releasing the radio resource configuration (e.g., radio resource configuration common, radio resource configuration dedicated). Also, the release of the SCell bearer may be performed by releasing one or both of a Data Radio Bearer (DRB) and a Signaling Radio Bearer (SRB) established in the cell 20.

The restoration (continuation) of the service B in steps S908 and S914 of fig. 14 may be performed by re-establishing a Packet Data Convergence Protocol (PDCP) layer and a Radio Link Control (RLC) layer corresponding to a bearer (e.g., radio bearer) established in the cell 20. Therefore, the restoration of service B in steps S908 and S914 may also be referred to as re-establishment or bearer reconfiguration.

The interface for the connection between eNB1 and eNB2 (e.g., LPN) or between eNB1 and eNB3 (e.g., LPN) may be an X2 interface between enbs or may be a new interface between enbs and LPN (e.g., X3 interface). Alternatively, the exchange of messages between eNB1 and eNB2 or between eNB1 and eNB3 may be performed by the EPC using an S1 interface.

(modification of Process example 3)

In the above-described process example 3, an example of transmitting the communication status information of the UE 4 on the second cell 20 from the eNB2 to the eNB3 via the eNB1 has been illustrated. However, alternatively, the eNB2 may send the communication system status information directly to the eNB3, without going through the eNB 1. In an example, the eNB1 may request the eNB2 to send communication status information for the UE 4 on the second cell 20 to the eNB 3. In this case, the eNB2 may send the communication status information to the eNB3 in response to the request from the eNB 1. In another example, the eNB3 may request the eNB2 to transmit communication status information for the UE 4 on the second cell 20. In this case, the eNB2 may send the communication status information to the eNB3 in response to the request from the eNB 3.

(Process example 4)

In process example 4, the processing of EPC5 is added to process example 3. Fig. 15 is an example of a sequence diagram illustrating the overall processing of procedure example 4. In fig. 15,

cells

10, 20, and 30 are denoted as cell 1, cell 2, and cell 3, respectively. The processing of steps S1001 to S1004 of fig. 15 is similar to the processing of steps S901 to S904 of fig. 14.

At step S1005 of fig. 15, the eNB1 sends a bearer switch request to the EPC5 (e.g., Mobility Management Entity (MME)) to change the bearer for the service B of the radio terminal 4 through the cell of the eNB2 to the bearer for the cell 10 through the eNB1 (path switch at eNB 2/cell 2 to eNB 1/cell 1 (for the service B)). Alternatively, eNB2 may send a bearer switch request to EPC 5.

The processing of steps S1006 to S1010 of fig. 15 is similar to the processing of steps S905 to S910 of fig. 14. At step S1011 of fig. 15, the eNB1 sends a bearer switch request to the EPC5 (e.g. MME) to change the bearer for the service B of the radio terminal 4 through the cell 10 of the eNB1 to the bearer for the cell 30 through the eNB3 (path switch at the eNB 1/cell 1 to the bearer (for the service B) of the eNB 3/cell 3). The processing of steps S1012 to S1015 of fig. 15 is similar to the processing of steps S911 to S914 of fig. 14.

(procedure example 5)

In process example 5, the processing of EPC5 is added to process example 3. However, process example 5 illustrates an operation different from process example 4. That is, in procedure example 5, the bearer of radio terminal 4 configured in the SCell before the change (i.e., cell 20) is directly changed to the SCell after the change (i.e., cell 30) without changing the bearer to the PCell bearer.

Fig. 16 is an example of a sequence diagram illustrating the overall processing of process example 5. In fig. 16,

cells

10, 20, and 30 are denoted as cell 1, cell 2, and cell 3, respectively. The processing of steps S1101 to S1104 of fig. 16 is similar to the processing of steps S901 to S904 of fig. 14.

Step S1105 of fig. 16 corresponds to steps S909 and S910 of fig. 14. That is, in step S1105, the eNB1 and the eNB3 perform preparation for using the third cell 30. At step S1106, the eNB1 sends a bearer switch request to the EPC5 (e.g., Mobility Management Entity (MME)) to change the bearer for serving B of the radio terminal 4 through the cell 20 of eNB2 to the bearer for the cell 30 through eNB3 (path switch to the bearer for eNB 3/cell 3 (for serving B) at eNB 2/cell 2). Alternatively, eNB2 may send a bearer switch request to EPC 5.

The processing of steps S1107 to S1109 of fig. 16 is similar to the processing of steps S905 to S908 of fig. 14. Further, the processing of steps S1110 to S1113 of fig. 16 is similar to the processing of steps S911 to S914 of fig. 14.

Other embodiments

The first and second embodiments described above may be applicable to a C/U separation configuration in which a macro cell having a wide coverage is used for transmission and reception of control plane signals (C-plane signals) such as mobility management of a UE, and a pico cell providing relatively better communication quality is used for transmission and reception of data plane signals (U-plane signals) such as user data. For example, cell 10 of eNB1 may be used for transmission and reception of C-plane signals, and cells 20 and 30 of

enbs

2 and 3 may be used for transmission of U-plane signals.

The first and second embodiments described above may be applicable when changing the primary cell (PCell) to another cell of the radio station (eNB)1 (e.g. a cell using a different frequency or arranged in a different geographical area). Also, the first and second embodiments may be applicable to a configuration in which there are multiple scells before or after an SCell change.

The first and second embodiments described above may be applicable to configurations in which the PCell and SCell employ different duplexing modes. For example, one of the PCell and SCell may employ Frequency Division Duplexing (FDD), while the other may use Time Division Duplexing (TDD).

All communication control methods executed by the radio station 1 (communication control unit 15), the radio station 2 (communication control unit 25), the radio station 3 (communication control unit 35), and the radio terminal 4 (communication control unit 45) described in the first and second embodiments can be realized by using a semiconductor processing device including an Application Specific Integrated Circuit (ASIC). Alternatively, the methods may be implemented by causing a computer system including at least one processor (e.g., a microprocessor, a Micro Processing Unit (MPU), a Digital Signal Processor (DSP)) to execute a program. Specifically, one or more programs including instructions for causing the computer system to execute the algorithms shown in the flowcharts and sequence diagrams may be created, and these programs may be supplied to the computer.

These programs may be stored and provided to a computer using any type of non-transitory computer readable medium. Non-transitory computer readable media include any type of tangible storage media. Examples of non-transitory computer readable media include magnetic storage media (such as floppy disks, magnetic tape, hard disk drives, etc.), optical magnetic storage media (e.g., magneto-optical disks), compact disk read-only memory (CD-ROM), CD-R, CD-R/W, and semiconductor memory (such as mask ROM, Programmable ROM (PROM), Erasable PROM (EPROM), flash ROM, Random Access Memory (RAM), etc.). These programs may be provided to a computer using any type of transitory computer readable medium. Examples of the transitory computer readable medium include an electric signal, an optical signal, and an electromagnetic wave. The transitory computer readable medium may provide the program to the computer via a wired communication line (e.g., an electric wire and an optical fiber) or a wireless communication line.

In the above first and second embodiments, the LTE system has been mainly described. However, the embodiments may be applicable to radio communication systems other than the LTE system, such as a 3GPP Universal Mobile Telecommunications System (UMTS), a 3GPP2CDMA2000 system (1xRTT, High Rate Packet Data (HRPD)), a global system for mobile communications (GSM) system, or a WiMAX system.

Further, the above-described embodiments are only examples of applications of the technical principles attained by the present inventors. It goes without saying that these technical principles are not limited to the above-described embodiments and may be changed in various ways.

The present invention is based on and claims the benefit of priority of japanese patent application No.2012-288212 filed 12/28 2012, the entire disclosure of which is incorporated herein by reference.

List of reference numerals

1 first radio station

2 second radio station

3 third radio station

4 radio terminal

5 core network

6 radio network

10 first cell

20 second cell

30 third cell

15 communication control unit

25 communication control unit

35 communication control unit

45 communication control unit

Claims

1. A first radio station for dual connectivity configured to operate a first cell, the first radio station comprising:

a transmitter configured to communicate with a radio terminal configured to perform dual connectivity using the first cell as a primary cell and a second cell operated by a second radio station or a third cell operated by a third radio station as a secondary cell;

at least one interface; and

at least one processor configured to:

sending a request to a core network via the at least one interface to change a radio station from the second radio station to the third radio station, wherein a network bearer of the radio terminal for data transfer between the core network and the radio terminal is established at the radio station,

wherein the network bearer corresponds to a secondary bearer established on the secondary cell for the radio terminal,

the secondary bearer is for data transmission via a radio station operating the secondary cell, and

the request includes General Packet Radio Service (GPRS) tunneling protocol (GTP) tunnel endpoint information.

2. The first radio station of claim 1 wherein,

the request is sent to a Mobility Management Entity (MME) of the core network, and the first radio station further comprises:

a receiver configured to receive a response to the request from the MME.

3. A core network for dual connectivity configured to communicate with at least a first radio station operating a first cell and supporting dual connectivity with a second radio station operating a second cell or a third radio station operating a third cell, the core network for a radio terminal configured to perform dual connectivity using the first cell as a primary cell and the second or third cell as a secondary cell, the core network comprising:

a receiver configured to receive a request from the first radio station to change a radio station from the second radio station to the third radio station, wherein a network bearer of the radio terminal is established at the radio station, wherein the network bearer is used for data transfer between the core network and the radio terminal via the radio station operating the secondary cell; and

at least one processor configured to perform a change of the radio station from the second radio station to the third radio station in accordance with the request, wherein the network bearer of the radio terminal is established at the radio station,

wherein the network bearer corresponds to a secondary bearer established on the secondary cell for the radio terminal, and

4. The core network of claim 3, wherein the core network has at least the functionality of a Mobility Management Entity (MME).

5. A mobile communication system for dual connectivity, comprising:

a first radio station configured to operate a first cell; and

a core network configured to communicate with at least the first radio station, wherein

The first radio station is configured to:

communicating with a radio terminal configured to perform dual connectivity using the first cell as a primary cell and a second cell operated by a second radio station or a third cell operated by a third radio station as a secondary cell;

sending a request to the core network to change a radio station from the second radio station to the third radio station, wherein a network bearer of the radio terminal for data transfer between the core network and the radio terminal is established at the radio station, and

the core network is configured to:

receiving a request from the first radio station to change radio station from the second radio station to the third radio station at which the network bearer of the radio terminal was established; and

performing, in accordance with the request, a change of the radio station from the second radio station to the third radio station at which the network bearer of the radio terminal is established, and

6. A method in a first radio station configured to operate a first cell for dual connectivity, the method comprising:

transmitting a request to a core network to change a radio station from the second radio station to the third radio station, wherein a network bearer of the radio terminal for data transfer between the core network and the radio terminal is established at the radio station,

7. The method of claim 6, wherein,

the request is sent to a Mobility Management Entity (MME) of the core network, and

the method also includes receiving a response to the request from the MME.

8. A method in a core network for dual connectivity configured to communicate with at least a first radio station operating a first cell and supporting dual connectivity with a second radio station operating a second cell or a third radio station operating a third cell, the core network for a radio terminal configured to perform dual connectivity using the first cell as a primary cell and the second or third cell as a secondary cell, the method comprising:

receiving a request from the first radio station to change a radio station from the second radio station to the third radio station, wherein a network bearer of the radio terminal for data transfer between the core network and the radio terminal is established at the radio station, wherein the network bearer is for data transfer between the core network and the radio terminal via the radio station operating the secondary cell; and

performing a change of the radio station from the second radio station to the third radio station in accordance with the request, wherein the network bearer of the radio terminal is established at the radio station,

9. The method of claim 8, wherein the core network has at least a function of a Mobility Management Entity (MME).